When light guide cables are used for telephone transmission, it is desirable in many instances to have the cables installed underground. Typically, the light guide cables are threaded through multiple duct conduit sections that are assembled at the job site, by connecting the conduit sections in end-to-end relationship at a level of about three or more feet underground to form a continuous conduit system. The conduit system extends from one manhole to another manhole, and the light guide cable is pulled through the inner ducts of the conduit system after the conduit system has been installed.
Typically, a plug or foam carrier is inserted into one end of one of the inner ducts of the conduit system, a pulling tape is attached to the plug, and the plug is propelled through the inner duct with compressed air, pulling the tape behind it. After the pulling tape has been threaded through a conduit system from one manhole to the next manhole, one end of the light guide cable is attached to the pulling tape and the cable is then pulled through the duct with the pulling tape.
It is more economical to have the conduit system extend for long distances between manholes so as to reduce the number of manholes necessary for a conduit system, and also to avoid the number of steps required in pulling the light guide cable from one destination to another.
In order to propel the plug that carries the pulling tape through the inner ducts of the conduit system, it is necessary that the inner duct segments be substantially sealed together so as to avoid the loss of air pressure as the air pushed the plug through the ducts. Moreover, it is desirable that the conduit segments be constructed so that they are easy to connect together and do not require extensive application of adhesives, tapes and other sealing and connecting devices.